Reticulon 4B (Nogo-B) Facilitates Hepatocyte Proliferation and Liver Regeneration in Mice

Nogo-B, also known as reticulon 4B, promotes liver fibrosis and cirrhosis by facilitating the transforming growth factor b (TGF-beta) signaling pathway in activated hepatic stellate cells. The aim of this study was to determine the role of Nogo-B in hepatocyte proliferation and liver regeneration. Partial hepatectomy (PHx, 70% resection) was performed in male wildtype (WT) and Nogo-A/ B knockout mice (referred to as Nogo-B KO mice). Remnant livers were isolated 2 hours, 5 hours, and 1, 2, 3, 7, and 14 days after PHx. Hepatocyte proliferation was assessed by Ki67 labeling index. Quantitative real-time polymerase chain reaction was performed for genes known to be involved in liver regeneration. Hepatocytes isolated from WT and Nogo-B KO mice were used to examine the role of Nogo-B in interleukin-6 (IL-6), hepatocyte growth factor (HGF), epidermal growth factor (EGF), and TGF-beta signaling. Nogo-B protein levels increased in the regenerating livers in a time-dependent manner after PHx. Specifically, Nogo-B expression in hepatocytes gradually spread from the periportal toward the central areas by 7 days after PHx, but receded notably by 14 days. Nogo-B facilitated IL-6/signal transducer and activator of transcription 3 signaling, increased HGFinduced but not EGF-induced hepatocyte proliferation, and tended to reduce TGF-beta 1-induced suppression of hepatocyte proliferation in cultured hepatocytes. Lack of Nogo-B significantly induced TGF-beta 1 and inhibitor of DNA binding expression 1 day after PHx and IL-6 and EGF expression 2 days after PHx. Lack of Nogo-B delayed hepatocyte proliferation but did not affect the liver-to-body ratio in the regenerative process. Conclusion: Nogo-B expression in hepatocytes facilitates hepatocyte proliferation and liver regeneration. (HEPATOLOGY 2013;57:1992-2003)